The Copper Chemical Garden as a Low Cost and Efficient Material for Breaking Down Air Pollution by Gaseous Ammonia

Chemical garden (CG) from copper(II) sulfate, nitrate and chloride (CG CuSO4, CG Cu(NO3)2, CG CuCl2) were grown and characterized from the structural and compositional point of view using scanning electron microscopy, X-ray powder diffraction, elemental analysis, thermogravimetric analyses coupled with mass spectrometry, and DR (Diffuse Reflectance) UV-Vis-Nir spectroscopy. The main crystalline phases, controlled by the anion of the starting salt, were brochantite and kobyashevite for CG CuSO4, gerhardtite, rouaite and anthonyite for CG Cu(NO3)2, and atacamite for CG CuCl2. The materials were then exposed to ammonia vapors to test the effectiveness of their entrapping property. All materials proved to be very efficient and rapid in the uptake of ammonia which invariably results in the formation of a Cu(II)/NH3 complex. However, after a few tens of minutes, CG Cu(NO3)2 and CG CuCl2 release water and get wet, thereby resulting unsuitable for applications. Only CG CuSO4 keeps dry for at least 25 hours. This makes it a valid candidate for building devices for trapping ammonia and possibly other gases capable of interacting with Cu (II). The entrapment of ammonia by this material was also characterized by 1H and 29Si MAS-NMR XAS spectroscopies.